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BMRI -San Luis Pit Backfi• CT Tests III I II I II I II IIII III • <br />TECHNICAL MEMORANDUM <br />DATE: 1 February, 1996 {~ <br />TO: Mr. Jim Dillie / Dr. Harry Posey(DMG) F~'® zt7 ~9y~ <br />FROM: Mark J. Logsdon (Geochimica) ~;,,;b;d~ d~ minerals & [ieo;otJY <br />Through: Sally Hayes (BMRI) <br />RE: HUMIDITY CELL TESTING OF PINK GNEISS - SAI+I LUIS <br />CC: A. Baldrige (BMG) <br />1.0 INTRODUCTION <br />Battle Mountain Resources (BMRI), Inc.'s San Luis Mine IS backfilling the deep <br />portion of the West Pit with waste rock from the "Pink Gneiss" unit under a <br />conditional approval of Technical Revision 18. Backfilling the pit will have several <br />beneficial effects on the Project area at the end of mining. Firstly, backfilling the pit <br />will buttress the high wall between the West Pit and Rito Seco, improving the long- <br />term geotechnical and hydrological performance of the reclaimed mine system. <br />Secondly, backfilling the pit will significantly reduce the amount of above-glade waste <br />rock that must be reclaimed at the end of mining. Thirdly, backfilling the pit will <br />reduce long-term consumptive water loss due to evaporation compared to the case of a <br />free-lake surface. The Division of Minerals and Geology (Division) have raised <br />questions about the geochemical and hydrological behavior of the backfilled pit that <br />must be addressed before the Division will authorize backfilling. <br />As part of its conditions for proceeding with backfilling, BMRI agreed to perform a <br />program of additional geochemical testing, as described in the memorandum, from <br />Geochimica/BMRI to the Division, dated O8 July 1995. This memorandum presents <br />and discusses the humidity-cell tests of Pink Gneiss samples; the samples and the <br />program were described in the July memorandum. <br />2.0 GEOLOGIC BACKGROUND <br />The weathering of waste rock is a hydrogeologic phenomenon, acting on geologic <br />materials. Properly, the evaluation of the potential weathering behavior of waste rock <br />begins with an evaluation of the geologic setting. <br />Geochimica, Inc 1 95021/1-Feb-96 <br />